Surface mounted, high pin count integrated circuit packages have been dominated by quad flat packs (QFPS) with various pin configurations, for example, leadless, J-leaded, and gull wing leaded. These packages have closely spaced leads for making electrical connections distributed along the four edges of the flat packages. These packages have become limited by being confined to the edges of the flat pack even though the pin to pin spacing is small. To address this limitation, a new package, a ball grid array (BGA) is not so confined because the electrical contact points are distributed over the entire bottom surfaces of the packages. More contact points can be located with greater spacings than with the QFPS. These contacts are eutectic or solder balls, which facilitate flow soldering of the packages onto a printed circuit board.
Sockets that accept BGA's are necessary for testing, burn-in, re-programming, but are becoming popular for production use on printed circuit boards where the integrated circuit may need replacing and where the replacing is difficult and endangers the integrity of the complete board. One obstacle to production use of BGA sockets is the cost of the socket. Such sockets have been developed to satisfy the testing and bum-in needs. But these sockets often prove too expensive to be used in production. One such socket is shown in U.S. Pat. No. 5,556,293 to Pfaff. Two other such sockets are shown in U.S. Pat. Nos. 5,578,870 and 5,646,447 referenced above. The first above patent uses three plates including a bias plate, while the other two use springs. Typically such designs will be too expensive for production use.
It is an object of the present invention to provide a BGA socket needing few and simple physical operations to insert and extract an IC package and suitable for production uses.
Another object of the present invention is to provide electrical connections from the ball leads to the socket contacts and then to the runs on a printed circuit card that are reliable and of low resistance. It is a related object of the present invention to provide a contact design that provides a gas tight, reliable connection to the ball lead.
It is another object of the present invention to provide a socket where there are mechanical forces of the BGA ball leads only and none on the BGA package itself.
It is yet another object of the present invention to provide a BGA socket with no obstructions that need to be avoided when inserting and removing the BGA package.